1. Field of the Invention
The present invention relates to a radiation imaging apparatus and a radiation imaging system.
2. Description of the Related Art
As a radiation imaging apparatus used for medical image diagnosis and nondestructive inspection using radiation such as X-rays, there has been commercially available a radiation imaging apparatus having an array of pixels each obtained by combining a switch such as a TFT (Thin-Film Transistor) and a conversion element such as a photoelectric conversion element.
Recently, studies have been made to develop multifunction radiation imaging apparatuses. One of such studies has been made on the incorporation of a function of monitoring radiation irradiation. This function enables, for example, the detection of the timing of starting radiation irradiation from a radiation source, the detection of the timing when radiation irradiation should be stopped, and the detection of the irradiation dose or integrated irradiation dose of radiation.
Japanese Patent Laid-Open No. 2012-015913 discloses a radiation imaging apparatus having a matrix of a plurality of pixels including pixels for radiation imaging and pixels for radiation detection. The pixels for radiation detection are used to detect the start of radiation irradiation (paragraphs 0074 and 0085), the detection of the end of radiation irradiation (paragraph 0094), or the detection of the cumulative irradiation dose of radiation (paragraph 0094).
In the radiation imaging apparatus disclosed in Japanese Patent Laid-Open No. 2012-015913, the signal lines connected to the pixels for radiation detection extend in the column direction, and non-negligible capacitances exist between the signal lines and the electrodes of photodiodes for radiation imaging. When the radiation imaging apparatus is irradiated with radiation, electric charges generated by photoelectric conversion are accumulated in the photodiodes of the pixels for radiation detection. Signals corresponding to the electric charges are output to the signal lines via TFT switches. On the other hand, when the radiation imaging apparatus is irradiated with radiation, photoelectric conversion also occurs in the photodiodes of the pixels for radiation imaging, and the potentials of the electrodes of the photodiodes change. With these changes, the potentials of the signal lines can change because of the capacitive coupling (crosstalk) between the electrodes and the signal lines via the capacitances. The signals appearing on the signal lines therefore include both signal components from the pixels for radiation detection and components generated by the capacitive coupling with the electrodes of the photodiodes of the pixels for radiation imaging. For this reason, the radiation imaging apparatus disclosed in Japanese Patent Laid-Open No. 2012-015913 cannot accurately detect signals output from the pixels for radiation detection.
Japanese Patent Laid-Open No. 2012-052896 discloses a radiation imaging apparatus including pixels for radiation detection, a plurality of radiation detection lines connected to each other, a plurality of noise detection lines connected to each other, and a radiation detection circuit. The plurality of pixels for radiation detection is dispersed, and each pixel for radiation detection is connected to any of the plurality of radiation detection lines. The radiation detection circuit detects radiation irradiation based on differences between the digital data obtained via the plurality of radiation detection lines connected to each other and the digital data obtained via the plurality of noise detection lines connected to each other.
In the radiation imaging apparatus disclosed in Japanese Patent Laid-Open No. 2012-052896, however, the sum of signals from all the pixels for radiation detection is supplied to the radiation detection circuit via the plurality of radiation detection lines connected to each other. For this reason, the radiation imaging apparatus disclosed in Japanese Patent Laid-Open No. 2012-052896 cannot independently monitor radiation for each set of a plurality of regions or portions.